Stoker



Aug 2, 19%.

W. M. SHWEHQKART T AL. 2

STOKER Original Filed Aug. 28, 1937 5 Sheets-Sheet 1 INVENTOR5 m 1% BY M BMMZW ATTORNEYS Aug, 0, 194.

W. M. SCK'iWEECKART Ema;

STOKER 01 iginal Filed Aug. 28, 1937 5 sheets sheet .2

INVENTORS ATTORNEYS WNW I ka.

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Aug 2Q, 1%46.

W. M. 5CHWEEKART ET AL, 2

STOKER 5 Sheets-Sheet 3 Original Filed vAu 28, '19s? F/PED 6. JUL m/v g 394% w. M. scE-zwEIcKART ET AL STOKER Origirial Filed Aug. 28, P937 5 Sheets-Sheet.- 4

[II ll I ll IIIIJ III ATTORNEYS v 'INVENTORS Aug. 20, 1946.

STOKER Original Filed Aug. 28, 1957 5 Sheets-Sheet 5 Tam 2a; A": I556, 6 I 281 23 eg g l 2/7 as j 2 4 INVENTORS RNEYS Patented Aug. 20, 1 946 STOKER William M. Schweickart and Fred G. Julyan,

Euclid, Ohio,

Company Incorporated,

poration of Virginia Original application August 28,

161,494, now Patent No.

ber 22, 1942. August 8, 1941,

This invention relates to improvements in automatic coal burners.

A primary feature of this invention is th provision of a burner that will burn different types of coking coal efficiently and economically, in small domestic installations as Well as in larger furnaces, and which is adapted to utilize various sizes of coal down to slack.

The burner is arranged to provide a novel combustion zone properly related to the feed so as to assure efi'icient coking, ignition and combustion of the solid and gaseous components without danger of back coking or clinkerformation at points that would interfere with the coal feed and efiicient combustion, arranged moreover to avoid the back flow of gas under appropriate operating conditions.

Another object is to provide a burner that will have high combustion efficiency, particularly when burning bituminous coal. The burner is arranged to produce a relatively thin bed of burning fuel, and to eliminate difliculties with clinker formation and ash accumulation which would tend to interfere with proper combustion. The ash removal mechanism removes the ashes and small clinkers rapidly and uniformly without interference with the fire bed, conveying them continuously to an ash discharge.

Another purpose is to improve the efliciency and control of the air supply to the fire. The forced draught is introduced in a zone at the top of the retort and outward over the grate, and is provided with an adjustment to meet the conditions of each installation as well as the varying fusion points and other characteristics of combustion of different types of coal. Under banking conditions provision is made for independent regulation of the air drawn by natural draught, permitting the efficient and certain maintenance of a suitable fuel bed.

An eincient electrical control system has been provided, which may be incorporated in combination with standard proven electrical devices. In general, the drive unit is controlled from the room thermostat and is protected b safety devices. An important feature of the invention is the provision of an efficient, sensitive and reliable banking control cooperating with the burner construction and the banking air control to assure the maintenance of a minimum fire by automatically providing fuel and forced draught accurately as needed.

An important object is to provide apparatus embodying features set forth herein which is simple, compact, strong, suitable for installation unassignors to Pocahontas Fuel New York, N. Y.,a cor- 1937, Serial No.

2,306,189, dated Decem- Divided and this application Serial No. 405,894

6 Claims. (01. 110-45) 2 der widely varying conditions operation.

Other objects and advantages of the invention will appear from the following description considered in connection with the accompanying drawings in which,

Fig. 1 is a perspective view of the assembly;

Fig. 2 is a longitudinal vertical section through the burner;

Fig. 2a is a plan view of broken away;

Fig. 3 is a detailed side drive;

Fig. 4 is a fragmentary view of the coal and air feed tubesand air control;

Fig. 5 is a fragmentary side elevation of the blower and air control viewed from the side of the assembly which is to the rear as shown in Figs. 1 and 4;

Fig. 6 is a diagram of an electrical control arrangement schematically applied to the burner assembly installed in a domestic furnace; and

Fig. 7 is a diagram illustrating the operation of the banking control switch shown in Fig. 6.

In the specific embodiment shown (Fig. 1) the apparatus comprises a drive unit B, a burner unit 0, and an ash discharge unit D.

A coal collector unit, not shown, ispositioned in the coal bin and supplies coal to the coal feed tube 22 in which is positioned the coal screw 2|, with the collector unit driven from the coal feed screw 2|. A suitable collector unit is shown and described in our Patent No. 2,233,085 granted February 25, 1941.

Where the conveyor tube 22 requires a bend. this is preferably made as an angle, for instance, a right angle, through a feed knuckle (not shown) provided for conveying the coal around the angle.

The drive unit B includes the motor with its controls, the blower and air supply, the drive for the coal feed and ash discharge screws, the grate rotor drive and gas withdrawal construction.

The drive assembly is mounted on a base 72 provided with a longitudinal cylindrical passage for the coal to which sections of the coal feed tube 22 are connected and through which the last section of the coal feed screw 2| passes. Supported upon the base 12 is the motor 15 having th rotor 11 of the blower 18 secured to one end of its shaft. A housing surrounds the blower air inlet, and air is admitted to the housing by the air inlet tube 82. The other end of the shaft of motor 15 is connected to the ash removal shaft 89 through reduction gearing contained within the casing 86 and through a sprocket and chaindrive including and economical in the burner with parts elevation of the grate the chain QI which engages a sprocket mounted upon the ash removal shaft 89. These connections may include a clutch operable from the handle I523 extending outside of the drive unit cover. 7

The burner unit C hereinafter described includes a rotating grate structure which is intermittently operated by reciprocating shaker rod its other end engaging ratchet Iii whichis ro-J tatably mounted on base 12 and is prevented from backlash b a silent detent cam H having an offset pivotal mounting III? on vertical Web II1 of the base 12 arranged so that the unbalanced weight of cam H5 will maintain its a surface in locking engagement with the teeth of ratchet I I4 to prevent backlash, lug I IE on amI I5 being positioned to engage the upper face o'f'web H1 when cam II5 is rotated out of engagement with ratchet H4, preventing cam H5 from being accidentally jarred or otherwise shifted into inoperative position. v

Means for regulating the throw of pawl II; and thereby varying the actuation of the rotary grate structure includes an upward extension H9 on pawl I I3 positioned to engage stop lllg I20 adjustably mounted as by a slot and a locking screw on web I I1 to control the length of the return throw of pawl H3. The lug I25 acts to swing the pawl H3 downward into engaging position with the ratchet H4. Cam roller III is suitably maintained in engagement with cai'n IIB, as by leaf spring I23 bearing against base 12 and rocker arm H2.

The intermittent movement of ratchet H4, which in the form shown is actuated twice during each revolution of sprocket engaged by chain 9!, is suitably transmitted to the ash grate, as by eccentric I24 mounted on ratchet H4 and carrying eccentric strap I25 on connecting rod I26 which may be connectedto shaker rod I59 by a suitable shock absorbing arrangement. For this purpose rod I25 may terminate in frame I21 in which the spring cage IE8 is mounted,.including end flanges I29 in which shaker rod I89 is slidably mounted, between which flanges shock absorbe spring I35 is set under initial compression and maintained in compressed condition b compression collar ISI held in suitable position on rod IE9 by stop pins I33 projecting from shaker rod I09 in position to engage the adjacent flange I29 and collar I3l under pressure of spring I35. Collar ISI is held against rotation by engagement with cage I28, and operates through clamp screw I32 to hold rod I09 in adjusted position. Cage I28 is preferably mounted removably on frame I21. This shaker rod spring construction will allow the stoker to run even though the grates are jammed, the restof the mechanism continuing to function normally and the placing, of the absorber spring I35 under initial compression is important to quiet operation.

This rotary grate structure surrounds an inner retort of the burner unit C of the type in. which the coal is forcedupwardly through the bottom edge onto the grate structure through which the ashes pass. In the arrangement disclosed the section of the coal feed tube 22 extending from the drive unit base 12 is clamped in the burner body I50 and supplies coal to the throat I5I at the bottom of the fire pot I52, which preferably is tapered outwardly from throat I5I.

The lower portion of pot I52 may consist of a pot wall I53 integral with burner body I55, and

a frusto-conical pot liner I54 having a smooth, preferably enameled inner surface, fitting within wall I53 and resting on a suitable ledge I55 to provide a smooth continuation of the surface of throat'I5L' A pocket I58 extending beyond throat I5I con- .centric with the axis of coal feed screw 2I has mounted therein a reverse screw I51. One end of this reverse screw is connected to the adjacent section of feed screw H by a connecting shaft I55 and the other end is connected to a terminal shaft I60 which extends through the bearing I59 at the end of pocket I55, the projecting end of shaft I55 having a sprocket 239 mounted thereon by means of which the terminal shaft I58, reverse screw I51, connecting shaft I58, coal feed screw BI and the mechanisms of the coal collector unit (not shown) are driven.

To provide for supply of air to the burning fuel, inlet air chamber I6! surrounds the pot wall I53, formed by bottom wall I62 and outer wall I53 and generally open at the top.

A suitable upper margin for the pot I52 is provided preferably in separable form and is generally referred to as a retort. While the retort may be formed and mounted in various ways, it is advantageous to provide a retort base ring I65 which may perform a number of functions. In the form illustrated ring I56 is held in position by bolts I61 threaded into lugs I64 on outer wall I53 of air chamber IBI, and may have 'a sealed engagement therewith by employing an asbestos gasket I63. Base ring I65 may likewise form a closure for the junction between pot wall I53 and pot liner I54, the form shown having an annular ridge I10 engaging a seal ring I69 of asbestos or the like located on the suitably beveled edges of wall I53 in liner I54. The ring I65 is provided with openings I'II (Fig. 2a) to permit the air from air chamber IGI to pass upthe upper portion thereof and traveling over the wardly to the retort.

The retort I12 is removably mounted on the base ring I65 and forms a continuation of the pot I 52, being provided with air outlets or tuyere's for furnishing air in the most advantageous zone for efiicient operation. In the form shown the retort I12 is provided with an inner wall I13 forming a continuation of pot I52 and the inner face of base ring I55, and resting on an asbestos gasket I14 in a suitable depression in base ring IE6. The outer wall I15 slopes outwardly and downwardly to thegrate structure, and rests on an asbestos gasket I16 in a suitable depression in base ring I65. The retort crown I11 provides an integral smooth curve between walls I13 and I15, and is preferably relatively narrow to revent retention of material thereon.

Suitable tuyre openings I18 extend through the retort I12 at appropriate points. It has been determined that the most advantageous construction comprises provision of a series of tuyere openings I18 in the upper part of the inner retort wall I13, preferably sloping slightly downward-and a smaller number of 'tuyere openings I18-extending through the upper part of the outer retort wall I15 at about the same level. The

retort I72 is held in place by means which preferably permits its ready removal and replacement, such as hooks I19 which may be cast integral with the retort walls I73 and I15, and which engage the lower face of the retort base rin I68 through suitable retort lock Openings,

The rotary grate structure located around the retort H2 is adapted to receive the burning coal and ashes which flow outwardly'over'the retort, sifting the ashes into a suitable annular receiver in which they are carried around the burner to a point of discharge. The various parts are carried by a-rotor ring I8I which is rotatably mounted on the pot I52 The mounting-of rotor ring IN on ball bearings is such that the parts may be readily assembled, the bearing will b easily accessible and the structure will function smoothly under the substantial variations in temperature and consequent expansion and contraction of the parts encountered under these conditions, the ball race being formed by cast surfaces. The arrangement comprises a ball race groove I 82 in the inner face of the upper part of rotor ring I 8I. An upwardly beveled flange I83 on wall I83 and a downwardly beveled flange I84 on base ring I88 are arranged to provide a ball race groove I85 cooperating with groove I82 to retain the balls I88. By the removal of retort base ring I68, the balls I88 will be readily accessible; and as the faces of grooves I82 and-I85 are substantially at 90 to each other, their spacing permits smooth unobstructed travel of the balls under various conditions of expansion due to changes in temperature.

The outer margin of the retort base ring I88 is provided with an apron I81 extending outwardly and downwardly over the upper edge of the rotor ring IIH, apron I87 providing a smooth path of flow for ashes around the ball bearing structure and beyond the outer face of rotor ring I8I, the adjacent faces of apron E8! and rotor ring I8I being suitably shaped to provide a relatively slight clearance and prevent substantial amounts of ashes from reaching the balls I 88, the opening I89 below said balls permitting any ashes or the like to fall out of the raceway. The annular pocket 233 below apron I81 accumulates ashes and an inner seal of ashes 234 is formed at the lower edge of the apron, restricting the passage of air to' the space above the grate.

In the embodiment shown a grate ring I88 is utilized, removably mounted on rotor ring I8I and adapted to receive removable grate segments I89. These segments are preferably flat integral castings provided with an inner flange I 98 extending into close relationship to retort base rin apron I87. Suitable slots permitting ashes to pass the segments I 89 include th radial slots I9I, restricted margina1 slots I92 in flange I98, preferably angled inwardly in the direction of rotation, and the spaces left between the periphery of each segment I89 and the adjacent parts.

Segments I89 are mounted on the grate ring I88 in suitable manner securely held in operation but permitting ready removal and preferably adapted to construction by casting. In the form shown each grate segment IE9 is provided with two downwardly extending slightly elongated annular sockets i93 adapted to receive supporting studs I94 on the upper margin of grate ring I88. An integral locking tongue on the advance end of each segment I89 extends'beneath a looking lug formed on the upper edge of grate rin I88. Grate ring I88 may extend to a point higher than the lower edge of apron I81, the intervening space normally filling with ashes, which form the air seal across the narrow slot between the apron margin and ring I8I.

beveled wedge lugs I 91 on rotor ring I8I engaging beveled wedge lugs I98 on grate ring I88 to force the grate ring downwardly into proper position by rotating it relative to rotor ring 'I8I stop lugs I99 onrotor ring I 81 and removable locking slugs 288 fitting between stop lugs I99 and wedges I98 when the grate ring I88 has been turned into proper position.

. The grate rotor structure is preferably provided with anash table 284, receiving ashes which pass the grate segments I89 and conveying such ashes to a point of discharge. A plurality of ash tablesegments 285 forms a continuous annular platform around rotor ring I8I adapted to receive the ashes. Each table segment 285 is provided with an inner flange 288 extending inwardly and upwardly, resting on an annular shoulder 281 on rotor ring I8I, the abutting edges of the table segments 285' being preferably in overlapping relationship to provid continuity and accurate registration. The lower rim 288 of grate ring I88 bears against flanges 288 and securely locks the table segments 285 in firm fixed position when the rotor ring and grate ring wedge lugs are interlocked as above described. Table segments 285 may be accurately located by positioning lugs on rotor ring I8I engaging corresponding positioning recesses in segments 285.

An ash trough extends around and below the ash table segments 285, for the direct discharge of ashes from the ash table. The ash trough 289 has an outer wall 2H1, a bottom 2II extending beneath and slightly spaced from the table segments 285, and an inner flange 2I2 extending upwardly substantially beyond the lower face of table segments 285. Segments 285 are preferably provided with diagonally tangential ribs 2I3 which serve to plow outwardly toward wall 2I9 ashes which fall between ash table 284 and wall 2I8, preventing the ashes from escaping over flange 2I2 while avoiding any engagement between the rotating and fixed parts. The ashes brushed outward by the ribs 2I3 accumulate at the outer edge of the bottom plate 2 and form an outer ash seal 28I at the periphery of the table 284 so as to restrict the flow of air to the space above.

The ashes carried around by ash table 284 are continuously discharged by a scraper 2M including an ash plow or vertical plate on the outer wall 2I8 of the ash trough extending into juxtaposition to the ash tabl 284 and grate ring I88 and deflecting ashes outwardly through a discharge opening 2I5 in wall 2 I8 into the ash discharge pocket 2I8 formed in said wall (Figs. 1 and 6). An ash discharge chamber 2I'I forms a downward continuation of pocket 2I6 and houses the receiving end of the ash removal screw 2I8 mounted on ash removal shaft 89 (Fig. 6).

A suitable arrangement is provided for supporting ash trough 289 and for connecting it to the furnace body. For convenience, trough 209 may be constructed in three segments, supported at the right of the burner (Figs. 1 and 2) by two bracket legs 228 overlying the two junctions of the segments and removably mounted on the 1; burner body I58 to permit convenient mounting and disassembly of the ash trough 209. The remaining junction between segments 2l'9 overlying the coal feed tube 22 is supported by a bracket 22l on the burner body I56, provided with a detachable clamp 222 overlying the junction and which may be detachably fastened to the bracket 22l. i

The upper margin of the ash trough 209 is connected to the furnace body to close the space between the body and the burner unit. This may be accomplished by providinga closure plate 224 resting on shoulder 225 formed at the upper margin of outerwa1l'2loof theash trough, and extending outwardly to the furnace walls. A suitable'filling or lagging 226, such as furnace cement or the like, maybe employed tofill the spaces between plate 224 and thefurnace walls, which are shown as comprising the usual water leg 221' of a domestic furnace. Plat 224 may be locked on shoulder 225 by segmental locking plates 228 fitting into an annular recess 229 in the upper margin of the outer wall 2) of the ash trough and provided with a longitudinal .rib 230.

The mechanism for rotating the grate unit employs an intermittent drive, imparting a. periodic impact to the. rotating structure, as such an arrangement serves to break up the fuel mass and. to facilitate the sifting of .the ashes and small clinkers through the grate. In the construction shown the shaker rod ")9 extends beneath the ash trough 2G9 and ispivotally con- 7 nected at its end to the lower'end of a feed dog arm 2 extending upwardly between the air chamber -|5| and the grate rotor ring l8l and having at its upper end a feed dog 242 projecting laterally between the support flange 243 on the inner face of rotor ring WI, and rack 244 on said ring overlying flange 243. The feed dog 242 is provided with "a rocking face 245 riding on flange 243, and suitable teeth 246 at its forward end adapted to engage rack 244. The arrangement is such that when the shaker rod lilois shifted to the left of Fig. 3 the dog 242 will be rocked on face 245 until teeth 245 engage rack 244, further movement of th shaker rod I69 serving to rotate ring l8l and the grate parts mounted thereon, while ring Hll will be free from dog 242 at the end of such stroke and during the return stroke of shaker rod H39 owing to the disengagement of teeth 24!; when the dog 242 is rocked in the reverse direction by continued travel of the grate rotor ring l8! under its own momentum or by the return travel of shaker rod I89.

To prevent reverse rotation of the grate ring l8! and associated parts a detent dog 241 is provided on detent arm 248 pivotally mounted on stud 249 on the burner body I50 at any convenient circumferential point and held yieldably in operative position as by counterweight 269.

Figs. 4,5 and 6 show the air supply and control system between the blower 18 and the burner unit C. The volume of air from blower 18 is suitably regulated, as by butterfly damper 284 mounted in air control housing 265 on spindle 266 preferably provided with suitable locking means, the form illustrated having a lockingdisc 261 mounted on the end of spindle 256 at the rear of housing 265 (Fig. 5) and held in adiusted position by locking knob 268 threaded on screw stud 269 extending through'concentric slot 210 andmounted on housing 265.

Means are provided for indicating the flow of air from blower 18,for preventing backflow into the blower system from the burner unit C, and for permitting aregulable-flowof air to the burner unit when the blower :is not in'operation. These functions may all be performed by a single mechanism comprising'a valve flap 2' fixed to pivot spindle 222 located in the upper part of a section of the air control housing 265 in advance of damper 264 and engaging 'valveseat 213, which is preferably inclined in the direction of air flow from the blower. The end of spindle-212 may be bent downwardly outside of housing 265 to form a pointer 214 serving in conjunction with suitable marks 215 or the like on the outer face of housing 265 to indicate the position of flap 211.

To arrest valve flap 21l at a predetermined preferably variable distance from seat 213 we provide a natural draft regulator spindle 216 threaded in housing 255, provided with a laterally extending stop arm 211 within housing 255 positioned for engagement with the face of flap 2H and serving as a variable stop for arresting the downward movement of flap 21! at any point between the valve seat 213 and the maximum desired opening of flap 21! by rotation of spindle 216 by means of knob 218, spindle 216 being frictionally held in adjusted position as by spring washer 219.

The air control housing 255 is connected to a suitable air duct 28B running to air inlet chamber 28! (Fig. 5) in the burner body I55, and merging, around the casing for the coal feed passage, with the air inlet chamber ISI to provide a, generally tangential air feed adapted to distribute the air evenly throughout the air chamber l6! and thence to tuyre openings I18.

A suitable arrangement is provided for automatically removing the ashes from the burner unit C and discharging them at an appropriate point, the construction shown including an ash removal conveyor and an elevator for transferring the ashes from the conveyor to a suitable discharge point. In the form illustrated the ashes are removed from the ash discharge chamber 211 by ash removal tube 285 mounted in the burner body l5!) and forming a continuation of chamber 211. Tube 285 extends to an appropriate point and is shown as terminating adjacent drive unit B (Fig. 1). At this point a suitable elevator unit D is positioned to receive the ashes. A convenient construction is disclosed, employing an arrangement in which the ash removal tube 285 terminates in an elevator pocket formed in elevator base 288. Ash removal screw 2H3 terminates at the pocket while the shaft 89 on which the screw is mounted extends through the pocket and a suitablebearing at the opposite side of the elevator base 268, and thence to the drive mechanism as already set forth.

An elevator tube 29:: is mounted in elevator base 288 extending from the elevator pocket upwardly in any desired direction to permit discharge at any appropriate point dictated by local conditions, the angle of tube 290 being readily adjusted by clamping base 288 in any desired rotated position about ash removal tube 285 through a suitable clampin screw. An elevator screw is positioned in tube 298 to pick up ashes discharged into the elevator pocket and raise them in tube 295 to a discharge at the upper end of the tube.

A suitable discharge arrangement is provided at the upper end of elevator tube 29:]. This may comprise a discharge head 3B8 mounted on the upper end of elevator tube 290 and carrying an upper bearing for the elevator shaft. Head 306 is provided with suitable spout discharge means, the illustrated construction employing two discharge spouts, each of which may be provided with a flexible tube 3I0 clamped thereto for di recting the ashes to any suitable receptacle, such as ash can 3I I (Fig.1). 7

A suitable arrangement is provided for driving the coal feed screw 2I from shaft 89. In the arrangement indicated shaft 89 extends through a bearing in chambe 2!! and a bearing on a bracket on burner body I50, and drives coal feed screw 2| through a sprocket on shaft 89, sprocket chain 240 and sprocket 239 mounted on shaft I60 to which the coal feed screw 2I is connected.

While various proportions and designs may be employed in the different parts of the apparatus disclosed herein, the proportions are of importance in various parts, and particularly in the burner structure, the size and proportions of the pot, retort, grate segments, ash slots in the spacing thereof, having been determined after substantial experiment as adapted to most efiicient operation with coking bituminous coal; and the drawings herein are drawn to scale to show the proper dimensional relationships between the various parts.

A suitable electrical control arrangement is illustrated in Fig. 6, and may be of the type in which the motor I5 is operated at full speed at suitable intervals, though the invention is not necessarily restricted to a control of this type.

Motor 15 is connected to the lin 320 by motor circuit 32I in which suitable motor protective devices are located, such as the overload cutout 322 and the thermal type cutout 323 which may include a heating coil 324 and a bimetal strip 325 adjacent thereto. The thermal cutout 323 may be mounted directly on the motor so that it may be affected rapidly by all conditions which cause overheating of the motor.

The motor circuit 32I includes the upper contacts 326 of duplex relay 32'! whose coil 328 is in line 323 passing through the secondary of the low voltage transformer 339 whose primary is connected across the main line 325. The main secondary lead 329 carries the protective and control devices in the heat generating apparatus, which in the present instance domestic hot water furnace 33I. In the form illustrated the line 329 carries a high point outout switch 332 operative to break the circuit when the heating medium has reached a predetermined temperature or pressure, and this line 329 also carries the banking control switch unit 333 hereinafter described. Line 3223 continues to the lower contact 334 of a room thermostat 335 of the type which includes a bimetal strip 335 operative when the room drops below the desired temperature to close contacts 333 initially and after a further temperature drop to close the connected upper contacts 331, thermostats of this type being well known.

The contacts 334 and 33? are connected through strip 333 and holding circuit line 338 with the lover contacts of relay 32? which connect with the main circuit 323. The upper room thermostat contacts 337 are connected through shunt circuit line 343 with the line 329 I at relay 327.

The banking control switch unit 333 is provided with two switches, a bank switch arranged to start motor I5 when additional fuel and air are required during banking periods, stopping motor 15 automatically after a suitable period; and an out switch arranged to stop motor I5 automatically if its operation under control of the bank switch does not result in a suitable pickup of the fire. These switches are operated is illustrated by a by a thermal element located suitably for prompt and sensitive reaction to changes in the temperature of the fire. There are extreme differences in such temperature between periods of maximum operation and the low fire bed which it is desirable to maintain under banking conditions when the effort is simply to maintain a minimum heating as in domestic installations in spring and fall.

Electrical control apparatus regulating the operation of motor I5 in connection with the house thermostat system may have appropriate parts thereof mounted as shown in control housing I33 (Fig. 1) carried by a bracket on drive casing 86. It has been found advantageous to locate the thermally responsive element of the banking control apparatus in the combustion chamber 34 I at a distance from the fire suflicient to permit the employment of a sensitive thermal device which will operate accurately with slight changes in temperature. For instance, such device may be located upon or at the furnace door mounted in suitable position .to be directly affected by both radiation and convection from the fire, without being influenced by various factors affecting temperature at other points in the furnace. Specifically, it has been found that the absorption and radiation of heat by portions of the furnace such as the water legs 22'! and 342, the variations in draught due to dampers and stack openings such as those shown at 343, and other variations in draught and temperature conitions seriously affect a sensitive thermal control unit located in the furnace at points other than the combustion chamber 3.

In the form shown the thermal element comprises a bimetal coil 335 arranged to extend through a suitable opening in the furnace door or other part of the furnace into position in the combustion chamber 34! where there will be no obstructions between thermal coil 345 and the fire in retort I12.

The thermal coil 3 l5is connected at its rear end to rotary switch rod 351. Switch arm 358 is centrally mounted on the end of rod 351 and is provided at its lower end with a clip carrying the mercury type bank switch 353. The mercury type out switch 35I is carried by a clip which is preferably mounted on arm 353 by means permitting the angular adjustment of switch 36I relative to switch 360.

Under certain circumstances, and particularly when burning certain types of coal, gases may be forced back through the coal feed tube 22, and an arrangement is provided for preventing the escape of such gases. Such an arrangementmay include a trap in which the gases will collect, and means for conducting the gases from the trap to a suitable discharge. In the preferred arrangement the gasesare conveyed to the burner. Owing to the relatively low velocity of such gases it has been found that under certain conditions there is a tendency for fine solid particles to accumulate in the return pipe and eventually to clog the pipe. The preferred form therefore includes means for preventing such accumulation of dust and the like, and for returning the gases to the burner or elsewhere by positive means, such as a suitable supply of air, which may be taken from the blower system.

An arrangement of this type is embodied in the preferred form illustrated herein, and is shown best in Fig. 4. It includes afresh air connection I35 with the outlet of blower I8 con nected by air pipe I36 and return bend I 37 with' jet nozzle I38 extending through a wall of the gas pocket I39 formed in the upper face of the coal feed passage 13 in base 12. The fresh air connection I35 thus utilizes a higher pressure from the blower than can be found anywhere beyond the damper control. A gas return pipe hi extends through the other side of pocket 139 in alinement with nozzle I38 and spaced therefrom by 'a distance suitable for obtaining an injector effect under the conditions of air pressure and dimensions employed in the arrangement. The gas return pipe M0 is connected to the burner unit C at the ash discharge pocket 216. Gas pocket I39 is sealed by a removable cover Ml.

While the apparatus is adapted for use with various types of coal it has been particularly designed to solve certain special problems encountered in the burning of bituminous coal, which has special characteristics affecting its collection, transportation and combustion.

The burner unit C is particularly designed to provide thoroughly efficient combustion both under active operating conditions during coal feed and operation of the blower, and under banking conditions. There is also secured a careful bal- -ancing between the rate of coal feed, the rate of air supply and the combustion characteristics of the coal, both as to the time required to burn to ash and the volatilization of combustible gases. The latter problem is especially important in the burning of" bituminous coal, and involves likewise the formation of coke, which heretofore has been a source of serious difiiculty and obstruction due to the tendency ofthe coal to coke back into the feed zone, interfering with the operation of the feed mechanism and frequently causing complete stoppage of the machine. The design also contemplates the effect of oil which is frequently used for dust prevention.

The rotating element I51 provided at the side of the throat opposite to the discharge end of the coal feed tube serves to prevent the coal from forming a packed mass at this point, and thereby increasing notably the facility with which it may be forced upwardly by the horizontal pressure of the feed screw. In one sense it may be said that this auxiliary screw increases the relative fluidity or flowing qualities of coal at this point. In the preferred form the rotating element is in the form of a' reverse screw exerting a counterbalancing horizontal pressure on the coal discharged by the feed screw while likewise preventing the formation of a solidly packed mass of coal, the result being that the coal will travel upward as gradually as may be desired without exerting any pressure whatever on the surfaces opposite the coal feed tube discharge. The reverse screw may be arranged to impel coal continuously away from the feed screw bearing, which may therefore be of any desired type. The elimination of the tendency to pack the fuel in throat l! furthermore permits the maintenance of fuel feed in tube 22 at substantially less than the full capacity of the tube as already indicated, since substantial. back pressure on the fuel at the burner owing to the resistance caused by forcing the fuel'upward under previous conditions causes the coal to back up along the feed screw; and even if. feeding at less than coal tube capacity is attempted, substanti'alback pressure at the burner and the resultant accumulation of coal in the tube "will'm'ake it impossible to operate the feed tubezlipartially filled at any point within asubstantial' distance of the burner. With the confor only a short distance from the burner, an arrangement which not only reduces to a minimum the power necessary for feeding at this most exacting point, but which also is desirable since a full feed tube 22 for a short distance from the burner is serviceable in forcing the gases to travel upwardly through the burner and not back through tube 22.

In burner retorts of the prior art difiiculties have been encountered because of the tendency of the coal under certain conditions to burn down in the pot toward the feed screw, resulting in the formation of coke and clinkers which obstruct the feed and burning of the coal and may result in breakage or stoppage of the mechanism. The travel of the coal upwardly in the pot may likewise be obstructed by the formation of clinkers and the like which adhere to the pot walls, and by mechanical obstructions provided by the wall surfaces. In the present construction a retort is provided in which the zone of active combustion is restricted to the upper portion, and which extends downwardly for a sufficient distance below the lowest point of air supply so that the fire will not reach the region where formation of clinkers, coke and the like will interfere with the feed mechanism. Any clinker formation developing will be prevented from adhering to the pot by the smooth liner I54 but will be forced upward and broken up by the incoming coal.

Under full draught conditions the relation between the coal feed and the rate of combustion is such that the burning fuel overflows gradually across the retort I72 and over grate segments I89, and may reach the Walls of the furnace. The relatively slight projection of the retort I12 above segments I89 facilitates the lateral flow, and is particularly advantageous in bituminous coal combustion in which the incandescent coke is more or less fluent, the arrangement permitting the formation of a relatively wide thin fire which produces maximum efficiency, rather than a high fire above the retort. The rate of combustion will naturally increase with the spreading of the fire until it will equal the rate of coal feed when the fire has reached its maximum area at the walls of the furnace. The inner tuyere openings I18 assure full combustion of gases which pass upwardly from the coking zone and provide an adequate supply of air for full combustion, the outer tuyre openings in wall I75 assisting if necessary in the combustion of the portion of the fire outside of the retort H2. The spreading of the fire is facilitated by the unusual power of the upward thrust of the coal, which likewise serves to scour away any clinkers which may tend to form on and adhere to the surface of the pot structure or retort I72.

When the drive unit is cut off and the fire operates under banking conditions, the portion of the burning coal beyond retort H2 will gradually burn up, and if banking conditions are maintained for a sufficient period, the fire area will gradually contract toward retort I72. Eventually the fire may contract to a zone in the upper part of retort H2 limited in depth by the distance that air will penetrate from tuyre openings H8. This arrangement, limiting the bank tuyere to a zone at the top of the pot substantially spaced from the feed Worm 2 l eliminates the possibility of coking back under banked conditions, a serious difficulty with prior arrangements. Atthe same time a small zone of definitely burning fuel is maintained so that when the drive struction illustratedhowever the feed tube isfilled 75 unit is again started and the coal feed is re- 13 sumed, there will be no difficulty about kindling promptly the green coal that is more or less abruptly forced upwardly in the pot I52.

When operating under banking conditions air is drawn through the tuyere openings I18 by the ordinary stack draught in a manner similar to the operation of hand-fired coal furnaces. This is made possible by the action of stop arm 21! which holds valve flap ZI'I open to the proper extent, thereby permitting the maintenance of a minimum bed of burning material without risking the extinguishing of such bed by insufiicient air, sudden influx of fuel or the burning out of accessible fuel by excessive draught.

The arrangement likewise is adapted to minimize the tendency to form coke in the lower portion of the pot where it might interfere with screw 2| through the depth of the pot, the aircooled walls and the double-wall construction. If however coke should form in throat I5I, it would not wedge between the screw and the end of the feed passage, as in prior arrangements, but would tend to be broken up by the rotary action of the feed screw 2| and reverse screw I51.

The rotary ash collecting unit is arranged to remove accumulations of ashes with a minimum disturbance of the fire bed. This operation is facilitated by the smooth-surfaced grate segments I89 and the intermittent shaking action imparted thereto. The formation of the described type of fire bed likewise facilitates the scouring of fine clinkers from the retort I12 and their discharge on to segments I83, which may be provided with slots sufficiently larg to receive the small clinkers as formed and to maintain a clean fire even under conditions which operate the burner at infrequent intervals. The ashes are effectively sealed in the ash receptacle and readily discharged from the burner in a manner already indicated.

Any gas which is formed will normally be generated so high in the pot I52 that it will tend to flow upwardly and to be burned; but in case gas is forced back through coal feed tube 22 it will be positively returned to the ash pocket ZIB by the action of jet nozzle I38, and will pass up; wardly to combustion past the grate segments I89. This arrangement will also provide a slight air feed outside of the retort I12 which will be operative to some extent when the blower I8 is not running, since the natural flue draught of the furnace will exert a certain suction effect on the gas return pipe I40. This arrangement also prevents any tendency for dust to collect in the gas return line.- It may be noted that when the valve flap 2l'I is allowed to fall upon its seat it provides positive means for preventing gases from the combustion zone from returning through the blower structure, if conditions should arise that demand such an arrangement.

The operation of the arrangement for conveying the ashes to a suitable point of discharge will be apparent from the detailed description. The construction is such that the ashes may be discharged at any desired point, and are kept completely housed in conveniently located conveying tubes.

The drive, operated by a single motor and compactly arranged, i constructed so that the blower permit throwing in the coal feed and ash removal mechanism abruptly after motor I5 is up to speed, exerting a sudden impulse that may be valuable in dislodging a slight obstruction. The apparatus is likewise arranged so that the motor I5 will be stalled before breakage of any of the drive parts, allowing the electrical system to throw out the motor circuit and take care of emergency conditions without damage to any part of the machine.

The blower structure has been carefully arranged to give rapid and accurate control of an adequate supply of air at all times without the usual excessive intake noise.

The general operation of the electrical control system will be understood from the specific description. Assuming that the building is at or above the desired temperature for which the room thermostat 335 is set, the motor 15 will be out of operation, since contacts 334 and 331 of thermostat 335 will be open and relay 327 will consequently be de-energized, opening the motor circuit at the upper contacts 326. When the thermal element 336 contracts due to reduction in room temperature thermostat contacts 334 will first be closed; and continued reduction in temperature will thereafter close contacts 331, completing the circuit between the line 329 and the shunt line 340, closing relay 327 and starting motor l5. At the same time the contact 333 of relay 321 will be closed; and as thermostat contacts 337 open when the room becomes warmer, motor I5 will continue to operate since the secondary circuit through line 329 will be completed by the holding circuit line 338 until the room is warm enough to open thermostat contacts 335,

whereupon relay 32? is de-energized and motor F5 will top. A sudden excessive load on motor Iii-will open cutout 322, while heating of motor 15 for any reason will operate thermal cutout 323, affording full protection to the motor. If the temperature of the heating medium should reach a point beyond which it is dangerous to continue, the high point cutout 332 will operate to break the main secondary circuit line 329, open relay 321 and stop motor I5. It is noted that as soon as the heating medium return below the danger point said circuit will be closed and the motor again started, assuming of course that the room thermostat 335 is in appropriate position with the contacts 334 and 331 closed.

The banking control unit 333 is arranged for operation at times when the room thermostat 335 is open; and such operation may be readily understood from Fig. 6. The thermal coil 345 will naturally expand and contract in accordance with the heat given ofi by the fire, thereby rotating switch rod 35! and the switch structure mounted thereon. The coil 345 is constructed and arranged so that the bank switch 360 will be appropriately positioned with the mercury out of contact with the terminals when the temperature in the chamber 3 is above a predetermined minimum banking temperature. As the temperature in said chamber approaches such banking temperature rod 35'! is rotated by thermostat 345 to turn the arm-carrying switches 36!) and MI and swing switch 350 downwardlyuntil the mercury flows to the contacts of both switches when such banking minimum temperature is reached'thereby closing an auxiliary circuit including conductor I26, switch 332, switch contacts 36%, 36L conductors 312, 340, coil 328 of relay 321 and conductor 329. The resultant closing of switch 360 completes a circuit through the banking shunt line 372 with the shunt circuit 340 andthrough the out switch 3B| with the main secondary line 329, energizing relay 321 and starting motor 15. The resulting increase in heat from the fire will rotate the switch rod 351 in the opposite direction until the bank switch 363 is turned oil by the flow of mercury from its terminals at the maximum banking temperature, thereby opening relay 321 and stopping motor 315. It is noted that this operation is independent of the thermostat 335, and is effective only when said thermostat is not closed.

The arrangement consequently serves to maintain a minimum banking fire independently of the house temperature control without interfering with the operation of such control and effective when such control is not active. It permits highly accurate and efiicient regulation of banking conditions, since it may be constructed for any desired range of banking temperatures, and the temperatures at which it operates may be readily adjusted by shifting arm 358. Furthermore, it is located at a point where it is affected promptly and directly by very small changes in the banked fire, and is sensitive to slight variations in temperature.

Out switch 36! is arranged and connected to stop motor 15 if the fire temperature should not rise after the motor has been turned on by switch 36!]. If the temperature in combustion chamber 34! drops to a predetermined extent below the minimum banking temperature, switch rod 351 will continue to rotate and tilt banking switch 36l until at a predetermined temperature the mercury will flow away from the contacts of switch 36l, breaking the circuit between bank switch 360 and line 329 and opening relay 321.

This arrangement is utilized to provide manual regulation of the coal feed and forced draught during starting of the fire. This is accomplished by pressing the button 3', closing contacts 368 and 363, short-circuiting the out switch 361 and starting motor 15, which runs as long as button 37! is pressed. If the fire ignites properly the heat will promptly affect thermal element 345,

which may be so sensitive that even very slight heat from the fire will be sufficient to close out switch 36l and permit release of button 31!. In igniting bituminous coal fires this period is extremely short, and may be two minutes or less,

since the unit 333 preferably operates at very low temperatures and thereby reduces to an absolute minimum the amount of coal burnt during nonheating bank periods.

The operation of control unit 333 cooperates with the setting of the main air damper 264,

which controls the forced draught, and the setting of valve flap 2', which controls the natural draught; since it is possible by employing a sensitive control directly responsive to changes in a very low fire, with an air regulating means especially suited for the maintenance of the fire steadily at such low point, combined with a forced draught regulation which appropriately builds up such small fire properly in a brief time, to provide a novel and highly effioient banking arrangement.

The air supply for the fire is intended to come mainly from the tuyere openings of the retort ring 115, and this supply serves in addition to maintain a proper cooling of the retort. Under running conditions substantially all of the air from the fan passes through the air spaces around the retort tending to cool it and prevent overheating and improper coking and clogging of the rising column of coal. Under banking conditions the natural draft draws air through the partly open valve flap 21! and damper 264 into the spaces around the retort and through tuyere openings I18 together with some slight leakage from the coal tube through pipe 143 and opening 2E6 into the space below the grate. There may also be some seepage of air through the ash seals for the rotor ring I81 and ash table 204. In this way the air supplied below the grates is negligible in amount, substantially the entire supply being through the tuyere openings of the retort both under running and banking conditions.

This is a division of our application Serial No. 161,494, filed August 28, 1937, now Patent No. 2,306,189 of December 22, 1942,

We claim:

1. A stoker combustion system comprising in combination with a retort expanding and opening upward, of means forming a combustion chamber above said retort adapted to be subjected to subatmospheric pressure by virtue of the fiue draft thereby effecting a natural draft of air into said chamber, means forming the bottom of said chamber and sealing it against entrance of air through the area around said retort including a stationary annular ash member and a grate structure movable around a central axis and comprising an annular upper grate surrounding the upper portion of said retort and a lower aSh table overlying said member, said overlying table cooperating with the overlaid part of said member to form an air seal, means for supplying coal to said retort and forcing it upwardly therethrough, and means for supplying air under pressure to the upper portion of the coal column in said retort, said means comprising a blower operable to supply air above atmospheric pressure and an air supply orifice for passing air to said upper portion of said coal column under predetermined conditions of banking aircontrol when said blower is inoperative and the combustion chamber is under pressure below atmospheric.

2. A stoker combustion system as set forth in claim 1 in which the retort and the grate structure have cooperating parts for trapping an accumulation of ashes and thereby forming an inner air seal.

3. A stoker combustion system as set forth in claim 1 in which the stationary ash member is annularly spaced from the outer surface of the retort so as to leave an air space therebetween.

4. Stoker apparatus as set forth in claim 1 having an ash removing conveyor and means cooperating with the air sealing means to form a substantially air tight enclosure beneath the grate for receiving the ashes sifting through the grate and conveying such ashes to and discharging them into the ash removing conveyor and for substantially preventing the passage of air from the furnace room to the furnace combustion zone by way of the furnace ash pit and the grate, thereby providing ash collection and removal while preserving the action of the banking air control when the blower is not in operation.

5. Stoker apparatus as set forth in claim 1 having ash collecting and removing means including an annular ash receiver positioned under the grate and rotatably supported upon the retort, an ash removal conveyor and means for rotating the ash receiver to transfer the ashes thereon to the entrance end of the ash removal conveyor, with the air sealing means of the banking air control including means forming an inner ash air seal between the ash receiver and the retort, an annular closure means closing the space between the furnace Walls and the grate and having an extension projecting downward below the grate, and means forming an outer ash air seal between the closure extension and the ash receiver, both such ash air seals substantially limiting the leakage of air from the furnace room to the furnace combustion zone by way of the clearances around the ash receiver incident to supporting the ash receiver for rotation.

6. A stoker combustion system comprising in combination with a central structure having a retort expanding and opening upward, of means forming a combustion chamber above said retort adapted to be subjected to subatmospheric pressure by virtue of the flue draft thereby effecting a natural draft of air thereinto, means forming the bottom of said chamber comprising an annular grate below the top level of said retort and having an inner edge overlapping said central structure and forming an ash seal therewith against the entrance of air to the combustion space, an ash ring carrying said grate and providing a lower ash seal substantially shutting off the air flow to the space below said grate around said ash ring, means for supply coal to said retort and forcing it upward therethrough, an air conduit for supplying air to the upper portion of the coal column in said retort under said natural draft and a blower adapted to force air through said conduit at pressure above atmosphere.

WILLIAM M. SCHWEICKART. FRED G. JULYAN. 

